15 degree switch question

WB3 · 02-21-2004, 07:26 PM

I'm trying to trouble shoot a cold start problem w/the CIS on my '83 SC. It's running lean (backfiring thru the pop valve) on start up. I tried measuring the resistance on the 15 degree temp switch but I got no reading. I disconnected the switch and tried to get a reading cold and also as the engine warmed up....it measured no resistance throughout warmup. Does this mean the switch is bad?

Also, the fittings on the fuel filter loosen in the "normal" CCW direction...correct?

thanks!

sammyg2 · 02-21-2004, 07:35 PM

I can't help on the temperature switch right now but i know the fittings on the fuel filter are standard right hand thread.

If you don't get an answer on the switch by tomorrow i can test the resistance on mine when I get home from work.

konish · 02-21-2004, 07:57 PM

Bill,
I suspect my 15 degree switch is also kaput, although I have to admit getting the tester leads down in that crack isn't the easiest...maybe I'll get some alligator clip type leads. Anyway, thers seems to be a disagreement between the Probst book on Bosch EFi systems and the Bentley manual. Probst says the switch is closed when cold, and the Bentely says open when cold. Either way, you should be able to detect when the thing actually swtiches. I am going to tackle this next as my car still has sputters the first 10-15 seconds, settles into a nice, 1200 rpm idle, but still acts a bit cold blooded.

R/
Dustin

WB3 · 02-21-2004, 08:18 PM

Thanks again Dustin, I had the time today and did a plug change along with trying to test that switch. You're right, getting the probe down there isn't easy. I taped the meter probe to a dowell type stick and it was no problem getting it in there. Just take care with the fan/belt spinning...hair, clothes, etc. One more interesting fact that I didn't mention in the orig post was that I used a test light on the wire that runs to the switch and it didn't lite (power on or with engine running). But then again, I really don't know if voltage is supposed to be going to it anyway. I would assume not since the switch is supposed to be sending the signal.

Thanks for the reply as well Sam. Those fittings on the filter were jam tight and I didn't want to push it without a line wrench. Just wanted to be sure of the direction. Thanks!

konish · 02-21-2004, 10:16 PM

Bill,
No voltage...just completes the ground for the lamda brain.
R/
Dustin

WB3 · 02-22-2004, 01:50 PM

Thanks Dustin. I don't know if this would have anything to do with the current problem but I think the fuel pump is getting ready to die. It has become louder lately and now it is not running steady. It has never cut off but it sounds like an angry "sick" bee or something. I have a new fuel filter that I wanted to install when I changed the spark plugs but I didn't have the proper line/flare wrench. I didn't want to chance damaging the fitting(s). But the pump really sounds sick....it was the worst today when I pulled in from work....like I said, it keeps running but it's not a steady hum. When it rain it pours....I guess I should change the filter ASAP and if that doesn't fix the unsteady running or sound...replace the fuel pump?

sammyg2 · 02-22-2004, 04:21 PM

I would pull the filter screen on the bottom of the fuel tank and check it first, if it is partially clogged it can make the pump cavitate and get noisier that heck, eventually leading to a failed pump.

konish · 02-22-2004, 04:51 PM

Bill,
Eventually all fuel pumps die, unfortunately, yours picked you to be the grim reaper. The PO of my car replaced the pump, and it works like a champ. When you do replace the pump, I would take a good hard look inside the gas tank too. If there is rust, I would have it blasted and sealed and replace the filter. CIS components are very sensitive to paritculants...especially the fuel distributor plunger...the plunger and bore are machined to a super small tolerance. You might find too that your pump may be effecting your lean condition as well...

R/
Dustin

WB3 · 02-23-2004, 08:55 PM

Hi Dustin & Sam,

I would like to thank you guys for your help and time thus far...I really appreciate it. I want to give you an update and ask a couple more questions if I may...

First, while coming home today, it felt like the car was starving for fuel. The fuel pump was still cavitating too. Anyway, I bought some flare wrenches after work and I got the filter changed tonight. After I got it changed (the old one was heavy...even with the fuel drained out), I pushed up on the plunger with the power on to prime the filter. I guess it still had some air in it because it took a bit to get it started and run. It seems to run smoother and I don't hear the pump cavitating. Earlier today the uneven running (cavitating) seemed to get worse as the engine warmed and I was driving and stopping in traffic and such. But I'll see how it runs tomorrow.

Another thing that I wanted to mention and ask you guys about...tonight after I changed the fuel filter and the engine was warming (and still running at low RPM) I pushed up ever so slightly on the plunger and the rpms went up and it started running smoother. I looked on the underside of the plunger with a mirror and could see some gunk built up on the very edge. Is it ok to spray some carb cleaner in there and wipe it down? What exactly controls the movement of the plunger and is it adjustable? If you adjust the idle does that move the plunger up?

While we're on fuel...I know you mentioned about the fuel or CO mix Dustin (the same right)? Anyway, is the mixture adjustment on the Right side of the fuel dist on the side (just below where all the fuel lines go into the dist? It looks like there's a 15mm or so nut and an allen type screw inside that? I would assume the nut is to lock the screw and keep it from drifting? If I'm correct, CW is to richen and CCW to lean?

Sam...you mentioned about cleaning the screen in the fuel tank. I guess I would need to drain the tank in order to clean it? Is it where the fuel line comes out of the tank?

I'm still stumpted on the 15 degree switch. But if I can't see any resistance on the ohm meter, I guess it's bad.

Thanks again & I will keep you posted.

vash · vash's Garage

you know, when you pushed the airsensor bar up, you kinda like richened the mix. just like as if the WUR lowered the system pressure to allow the bar to move up easier. during start up cold the system pressure is lower to allow a richer mix, and as the car warms it increased pressure to the plunger to restrict and lean the mix. have you hooked the car up to the CIS tester guage yet? that can tell you everything you need to know. i am still learning myself.

cliff

WB3 · 02-24-2004, 06:18 AM

Hi Cliff,

No, I haven't tested the system pressure yet and now I know it's the first step when troubleshooting the CIS system. I'm still learning too. Trouble is, this car is now my daily driver as my back up car is down with a collapsed lifter (I think). I was outside in the rain (under a tarp) changing the fuel filter until 12:30 last nite. Before, it was taking about three cranks to start (and run). And it ran poorly until it warmed up. This morning it took about 6-7 tries to get it running. The main problem being the backfiring through the pop valve and low rpm. I didn't even chance going to work and took the day off. What seems very odd is that this problem raised its head the morning after the diode/rectifier went south on my alternator. I got that fixed and haven't had any more problems with it. I have read in one or two previous posts about a relay under the passenger seat? I assume it has something to do with the brain and lambda system. Anyway, they said that if you disconnected the relay with the engine running that the engine should run very poorly. I have done this and I notice no differance..none at all. Maybe this relay is bad and is throwing the whole system out of wack? Come to think of it, I remember a noise emitting from that area (under the passenger seat) awhile back and it didn't sound right. I bet it was that relay. I think your system and mine are different and you don't have all the components that Porsche added over the years. I've got an '83...the last year of CIS. And as I'm learning, the most complicated to boot.

I've changed the WUR, fuel filter, looked for vacume leaks, and still no joy. Like many fellow owners in here, I feel like I'm banging my head against the wall. Anyway, thanks for the input Cliff.

Bill

WB3 · 02-24-2004, 06:24 AM

As an added note, how do you rid the fuel system of air once you open the system? Such as a filter change. Maybe that's why it took more cranks to get it running...because there's air in the fuel system.

john walker's workshop · 02-24-2004, 08:01 AM

sounds like you just have to richen the mixture to smooth out the idle. the proper way is to use a CO meter at a shop. the mixture screw is reached by inserting a fairly long 3mm allen wrench down the small hole between the fuel distributor and big ribbed rubber air boot. turn clockwise just a hair and see if the idle inproves. without the CO machine, you can listen for the idle to get better as you turn the adjuster just a tiny bit at a time, but don't go beyond the point where it just gets nice, and you'll be in the ballpark. you will probably have to turn down the idle speed as the mixture is richened. don't forget to see if the oxygen sensor relay is working the frequency valve first. unplug the relay under the passenger seat. if the idle gets rough, it was ok. also, the fact that it starts means the cold start system is ok, regardless how it runs after it starts. poor run after starting is another issue, like a lean mixture, or incorrect tuneup adjustments, or a variety of other things.

Superman · 02-24-2004, 08:48 AM

There is a specific way to troubleshoot CIS systems. It's a step-by-step process involving a pressure tester.

But the most popular method of troubleshooting by home mechanics is to GUESS and REPLACE EXPENSIVE PARTS. This method is not popular because of its low cost or its effectiveness, in fact this method takes the longest and costs the most. But if you're not going to follow the prescribed troubleshooting method, and if you're going to guess, then my advice is to listen to John.

WB3 · 02-24-2004, 01:20 PM

Thank you Superman for your reply and advice. John, you nailed it. Mookster, you were right on as well. Eureka!!! Problem solved!!! I would never have guessed that such a vital circuit would be wired into the interior lights...glovebox, dome, hoodlight, etc. Man, I am so happy now I can't tell you!!! All this over a 5 amp fuse. I started to think back...when the rectifier on the alternator went south that's when I was opening the hood alot and the interior fuse blew. Turns out, the switch that turns the hood light on and off was shorting out and blowing the fuse. The 02 relay wasn't bad it just wasn't getting any power. Man!!!!

Anyway, I robbed the 5 amp license plate light fuse and plugged her in. In ONE crank the engine fired and the difference was noticeable right away. No more backfiring through the pop valve and it sounded right on! Idle is rock steady @ 1000 rpm. Throttle response is smooth and beautiful once again. I am overjoyed!

I would like to THANK each and everyone of you that responded to my thread...all three of them. Even if your advice did not help me solve this problem, I still thank you very much for your time, effort, and advice. This is a really, really, great forum to have! If I could take you all out to dinner I would! Thank you again everyone, and special thanks to John Walker, Mookster, Konish, Doug Zielke, Gram Archer, and Sammyg2. You guys are great!

HORRAAAYY!!! THREAD(S) ARE CLOSED AND HOPEFULLY THE HISTORY CAN HELP SOMEONE ELSE!

Thanks again!
Bill

vash · vash's Garage

WB3! great job!

konish · 02-25-2004, 05:39 PM

WB3,
I too have been running down my own CIS issues. I has a sneaking suspicion that my car had been tuned to run without the freq valve as pulling the relay under the seat had no effect on the way the car runs. Anyway, after running through all the connections, I traced the freq valve connection to the 18 pin (?) connection right next to the left shock tower. After pulling it apart, I was able to determine that the connection from the freq valve was good (good continuity), and there was power being supplied to the appropriate pins (around 13 volts). I cleaned and hooked it all back up and voila!, I could hear the valve just a buzzin'away. I shut the motor off, and with the ignition "on", I lifted the air sensor plate and confirmed that it indeed is alive. I will say that the idle hunts now as the car had been tuned to run without the valve...probably lean now. Anyway, the only thing I could not confirm was the duty cycle. I borrowed a dwell meter from a friend, which has a 8 cyl and 6 cyl scale. On the 6 cyl scale, I saw only about 30% duty cycle...not sure if this is due to my meter or maybe a bad lamda control box (according to Probst anyway). I'll do some more tuning...

R/
Dustin

WB3 · 02-25-2004, 06:24 PM

Hi Dustin,

Yeah, electrical can be a real hugger mugger and it's not one of my strong points. But that's great that you got that figured out. I'm glad I didn't go as far as to start messing with the mixture. I knew it had to be something else. I didn't think the mixture could go that far off. And it sounds like the PO or someone tuned your car to run without the FV...instead of finding the root cause. And it sounds like you found it in that connector. Wow. Yeah, it sounds like you're going to have to get it tuned right again.

While I had my Lambda brain out I took the cover off and looked inside. I was expecting something really wild but it was just a circuit board. The outside of the box is pretty scruffy but the inside was as clean as a whistle. Great that you got that figured out though...sure is a good feeling!

Speedy1 · Speedy1's Garage

I have simmler issues my wrench told me that the aux air valve may not be working so at start up cold she fires right up but has a very low idel no fast idel . then just this week she starts surgeing after start up 1200 rpm to 400, when warm yahoo all ok any info ? oops sorry 82 sc

WB3 · 02-26-2004, 02:08 AM

Hi Speedy,

Yes, could very well be the AAV. It's the aluminum jobby mounted just above #4 & #5 cyl on the RH side. It has an electrical plug going to it. They're supposed to be open when cold and close as the engine warms up to operating temp. Sometimes they get stuck closed. You can take off the outside hose and look in there with a mirror and flashlite and see what's happening with the valve. I would make sure you're getting power to the elec plug as well. Just use a cheap test light for that. Oops! gotta go to work. Good luck and hope this helps!